1. Field of the Invention
The present invention relates generally to the capture of data from data bit streams.
2. Description of the Related Art
The market for digital displays (e.g., flat-panel displays) has rapidly expanded in recent years. Because the existing base of cathode ray tubes require analog data, however, these digital displays must maintain compatibility with existing analog data interfaces along with the newer digital data interfaces. Accordingly, the Digital Display Working Group developed a digital-visual-interface (DVI) specification which controls the implementation of analog and digital data interfaces. The analog interface references the Video Electronics Standards Association (VESA) standard for computer displays and the digital interface references the transition-minimized-differential-signaling (TMDS) format in addition to others such as low-voltage differential signaling (LVDS) and gigabit video interface (GVIF).
DVI encodes original 8-bit graphics data to a TMDS stream of 10-bit dc-balanced, transition-minimized words. In particular, a DVI algorithm encodes the data to minimize transitions and adds a bit to indicate which of two methods was used to describe the transitions. The algorithm also effects an approximate DC balance for the data stream by selectively inverting words and then adding a tenth bit to indicate the inversion used. Data channels 0, 1 and 2 (e.g., red, green and blue data) are each carried on a respective one of three TMDS streams. Horizontal and vertical sync signals are coded on the blue channel during blanking periods and additional control information is generally coded on the red and green channels during the blanking periods.
Because each 8-bit graphics word has been converted to a 10-bit serial word, DVI data rates can be as high as 1.65 Ghz with transition times on the order of 100 picoseconds. Although the encoded data streams are generally carried in 50 ohm shielded twisted-pair cables and impedances along the cables are well matched to reduce reflections, the accurate detection of these narrow pulses and the corresponding capture of their encoded data is a challenging task.